MS Word Automation in C# - Unable to cast object of type 'System.String[*]' to type 'System.String[]'

Question

I use this code to get a String array of headings used in a MS Word 2007 document (.docx):

dynamic arr = Document.GetCrossReferenceItems(WdReferenceType.wdRefTypeHeading);

Using the debugger, I see that arr is dynamically assigned a String array with titles of all my headings in the document (about 40 entries). So far so good.

Then, I want to access the strings, but no matter how I do it, I get the following exception:

InvalidCastException: 
           Unable to cast object of type 'System.String[*]' to type 'System.String[]'.

I have tried different ways of accessing the strings:

By index:

String arr_elem = arr[1];

By casting to an IEnumerable:

IEnumerable list = (IEnumerable)arr;

By using a simple foreach loop:

foreach (String str in arr)
{
   Console.WriteLine(str);
}

However, no matter what I try, I always end up with the same exception as shown above.

Can anyone explain what I am missing here / what I am doing wrong? And especially String[*] - what does it mean?

Answer 1

string[] is a vector - a 1-d, 0-based array. string[*] , however, is a regular array that just happens to have one dimension . Basically, you are going to have to handle it as Array , and either copy the data out, or use the Array API rather than the string[] API.

This is the same as the difference between typeof(string).MakeArrayType() (the vector) and typeof(string).MakeArrayType(1) (a 1-d non-vector).

Answer 2

try

object arr_r = Document.GetCrossReferenceItems(WdReferenceType.wdRefTypeHeading);
Array arr = ((Array) (arr_r));

string myHeading = (string) arr.GetValue(1);

Answer 3

The problem is that you're using dynamic in a situation where it apparently wasn't intended. When the dynamic runtime sees a 1D array, it assumes a vector, and tries to index into it or enumerate it as if it were a vector. This is one of those rare cases where you have a 1D array that is not a vector, so you have to handle it as an Array :

Array arr = (Array)(object)Document.
            GetCrossReferenceItems(WdReferenceType.wdRefTypeHeading);
// works
String arr_elem = arr.GetValue(1);
// now works
IEnumerable list = (IEnumerable)arr; 
// now works
foreach (String str in arr)
{
    Console.WriteLine(str);
}